7158

• UCREFRP Catalog Number: 7158
• Author: Hickman, T. J.
• Title: Effects of Habitat Alteration by Energy Resource Developments in the Upper Colorado River Basin on Endangered Fishes.
• USFW Year: 1983.
• USFW - Doc Type: 537-550
• Copyright Material: YES

(1 , .
This impediment may have a profound effect upon the survival
of the Colorado squawfish. Such migrations appear to be
related largely to flow, temperature, spawning, and feeding.
Dams of various types upstream from Glen Canyon Dam have
obstructed access to approximately 396 km (246 mi) of the
available habitat in the upper basin. Access to another 216
km (134 mi) of the upper basin could be restricted with the
con~truction of the ~roposed White River Dam and the proposed
Jun1per-Cross Mo~nta1n Dam on the Yampa River. Approximately
550.3 km (342 md of the Upper Colorado River system have
been impou.nded. Another 319.4 kIn 098.5 mi) in the Upper
Colorado R1ver system have been proposed for impoundment.

Molles [9] suggested that the fragmentation of the
Colorado River system by dams might isolate subpopu1ations
and restrict gene flow of the endangered fishes, thereby
reducing the ability of these subpopu1ations to adapt to
changing environmental conditions.

Subtle impacts, poorly understood and difficult to
assess, are those associated with changes in the natural
hydraulic cycle with its normal seasonal extremes that were
once the pattern of the Colorado River. For example, spring
peak flows have been reduced below Flaming Gorge Dam by 50%
and baseline flows for the remainder of the year have
been increased by 140%. This picture is further complicated
by the highly variable daily fluctuations in flow.

This radical alteration in annual flow patterns results
1n submerging and exposing of the endangered species habitat
on an annual basis, which impacts important spawning and
foraging areas. Holden [10] suggested that the new flow and
temperature regimes below Flaming Gorge Dam were probably the
major factors in eliminating the bony tail chub from that
area. Suttkus and Clemmer [11] indicated that the future of
the humpback chub in the Grand Canyon is questionable due
to altered flows and temperature, which fluctuate more than
historic conditions.

There are usually significant changes in temperature
regimes, turbidity, salinity and other water quality factors
below dams. Generally, mean temperatures are often reduced
turbidities decline and salinities increase [10,12]. All of
these changes can have a dramatic effect upon the survival of
the endangered Colorado River fishes for several miles below
the impoundments.

dam
and

Releases of cold water from Flaming Gorge Dam, after the
was closed in 1962, effectively eliminated squawfish [1]
bony tail chub [13] from 105 km (65 mil of the Green River

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below the dam. Subsequent pe.nstock modifications on Flaming
Gorge Dam have resulted in the release of warmer downstream
water. This modification may serve to lessen the impact of
adverse water qualities below Flaming Gorge.

Much of the Colorado River system has been "tamed" by
impoundments, giving a compet it ive edge to introduce fishes
which now predominate in much of the system. Only in the few
relatively natural riverine stretches do the native species
retain their dominance. Impoundments have created a refuge
for exotic fishes that otherwise might not be able to com-
plete their life-cycle in the absence of a 1entic or reduced
flow environment. The impoundment of additional river
reaches will result in a still greater proliferation of
exotic species in the upper basin, the impacts of this
proliferation on the behavior and survival of the remaining
populations of endangered fish species in the Colorado River
basin is not easily predicted.

Colorado squawfish, humpback chub, and bony tail chub are
not known to reproduce successfully in lentic habitats.
Colorado squawfish can live in reservoirs but they have been
unable to maintain themselves by natural reproduction [1].

Water Depletion

Water depletions from the Upper Colorado River Basin
have drastically altered flow patterns, water quality parame-
ters, and river channel characteristics, and eliminated the
quiet backwater nursery areas to a point that much of the
essential habitat for endangered fishes is no longer present.

Flow depletion in the upper basin may have immediate and
long-term effects on the endangered fish. The immediate
effect is loss of flow and reduct ion of required habitat.
The depletion of water during peak runoff periods may lower
'" \ overall reproductive success of the fish.es. Flows belo~ an
'c.'< \ u nk n own c r it i c a I 1 eve 1 c ou 1 d res u 1 t 1 n 10 s s 0 f h a b 1. tat
~y) ! concentrating the endangered fish populations, thereby
increasing the danger of disease and predation by other
'-fish.

,

Long-term effects of flow reduction change the hydraulic
characteristics of the river thus altering stream bank cut-
ting, meander patterns, backwater building, sediment trans-
port capacities, and velocities. With time, eddies, pools,
riffles, river banks and beds can be greatly changed along
with channel depth, width, and flow patterns. These changes
as well as changes in temperatures and turbidities may affect
reproduction and other life history stages. The gradual,

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